Transcript Climate Change

The essential
science behind
Climate Change
– for students and
teachers
Jenny Pollock
HOD Earth & Space Science
Nelson College for Girls
[email protected]
July 2016
Two Adelie penguins stand atop a block of melting ice on
a rocky shoreline at Cape Denison, Commonwealth Bay, in
East Antarctica January 1, 2010.
PAULINE ASKIN/REUTERS
What is the difference between climate and weather?
Weather is the term we use for short-term atmospheric conditions at a particular
time and place – eg cold, windy and rainy in Wellington today.
Climate is average weather for a city, country or the whole planet over years.
Put simply – climate tells you what clothes to buy but weather tells you what clothes to wear.
Climate change happens when there are changes
to average weather.
Climate varies over years with natural cycles/events
(eg El Nino/La Nina cycles or volcanic eruptions)
Changes over decades to thousands of years
are caused by changes in greenhouse gases in the
atmosphere from both natural and human activity.
The world's climate varies naturally over millennia as a result of:
• Changes in energy received from the sun
• Changes in the blanket of greenhouse gases
• Changes in the Earth's orbit and tilt of its
axis (affects solar energy reaching earth)
• Absorption of heat by the oceans (over 90%)
• Tectonic plate movement causing changes in ocean
circulation, mountain building and volcanic activity
Climate has cooled (~13°C) naturally over the last 50 million years, and varied in
100,000-year warm-cold cycles (the Ice Ages ~5°C) over the last million years.
However, there is very strong evidence that the 1°C warming of the last ~100 years
can’t be explained just by natural causes. The concentration of greenhouse gases in
the atmosphere has risen especially because of the burning of fossil fuels and
deforestation.
Modern Climate Change is also called Global Warming, because Earth is now slowly warming.
The evidence for this comes from many sources – see slide 17.
Fossil Fuels
http://tunza.ecogeneration.org/editorPhoto/
clip_image002_0011.jpg
Fossil fuels are the remains of once
living organisms that were fossilized
and changed into coal, crude oil
and natural gas 10’s to 100’s of
millions of years ago. Burning fossil
fuels over the last decades and
centuries has resulted in fossilized
carbon being released into the
atmosphere as carbon dioxide.
http://s18.postimg.org/x
9e9fytnt/oildrill.png
Some of the evidence for Climate Change and Global Warming
Increasing temperatures — Global temperature averages over the last 100 years by
NASA and the Hadley Centre show the Earth has warmed by about 1°C, mostly in the
last four decades. Oceans have also warmed by absorbing over 90% of the sun’s heat.
Changes in rainfall — Rainfall patterns are changing across the globe with increasing
floods and droughts. There are also changes between seasons in different regions.
Changes in nature — Growing seasons have lengthened with spring starting earlier and
autumn/winter later. Many species are changing their behaviour and where they live.
Sea-level rise (SLR)— Sea-levels have risen about 17 cm (global average) since 1900
because of thermal expansion of ocean water and melting glacier ice. SLR has
increased from ~1mm/year 100 years ago to 3 mm/year today.
Glaciers all over the world are retreating, but outside the polar regions these can add
<0.5 m to SLR. The polar ice sheets (Greenland and the Antarctic) store water
equivalent to 7 and 57 m of Sea Level Rise respectively, and started to lose mass in the
1990s. At present they contribute only 1mm of SLR/year, but satellite measurements
show ice loss is accelerating which could raise SL ~1m by 2100.
What is causing the Climate to change?
The Earth is getting warmer because humans are adding heat-trapping gases to the
atmosphere, mainly by burning fossil fuels. These are called greenhouse gases(GHGs).
Which gases are greenhouse gases?
The main ones are:
Carbon dioxide: released naturally (e.g. volcanoes, decaying
plants/animals, respiration. Also from burning fossil fuels.
~76% of emissions. Persists for millennia; ~ 20% left after 10,000 years.
Methane: released naturally by decomposition in swamps, from
ruminants, especially cows, and leakage from fossil fuel extraction.
~16% of emissions. More effective than CO2 but less abundant.
Critically, it loses its effect when it breaks down after ~10 years.
Nitrous oxide: released mainly from agricultural fertiliser.
~6% of emissions. Breaks down or absorbed after ~100 years .
Water vapour: also a GHG but water is everywhere, and warmer air
carries more vapour. Water vapour doesn’t drive but amplifies warming from other GHGs
But – first of all – what is ‘normal’ or ‘natural’?
We need a certain amount of GHGs.
If it were not for greenhouse gases
(carbon dioxide, methane and nitrous
oxide) trapping heat in the
atmosphere, the Earth would be a
very cold place. Greenhouse gases
keep the Earth warm through
this greenhouse effect.
The GHGs form an invisible layer in the
troposphere – the bottom layer of the
atmosphere.
Note: It is (long wave) infrared radiation
given off by the Earth that is trapped by GHGs
(NOT solar radiation).
http://www.dpi.nsw.gov.au
/content/education/resour
ces-for-schools
The Earth gets solar
energy as sunlight
(shortwave radiation). The
Earth's surface absorbs
some of this energy and
heats up, but then cools
down by giving off a
different form of energy,
called (longwave)
infrared radiation.
Some of this radiation
escapes to outer space,
but most is absorbed and
re-emitted by GHGs
which makes the
atmosphere warmer. This
makes the Earth's surface
warmer, too.
More on the Greenhouse Effect
If greenhouse gases are normal what is going wrong?
• Humans are adding extra CO2, CH4 and nitrous oxide to the atmosphere.
• Synthetic greenhouse gases are also being added such as CFCs plus sulfur
compounds. (CFCs deplete ozone in the stratosphere but when they are in the
troposphere they act as GHGs).
• CO2 is produced the most and it causes most of the warming. At the
moment the ocean is absorbing large amounts of CO2.
• As fossil fuel usage increases (such as the burning of coal, oil and natural
gas), the amount of these gases in the atmosphere rises.
• Humans have interfered with the carbon cycle (e.g. by burning forest
lands, or mining and burning coal), and have moved carbon from solid
storage to its gaseous state, increasing atmospheric concentrations.
How do we know that there is extra CO2 in the atmosphere?
The evidence for this comes from atmospheric measurements of carbon
dioxide in the northern and southern hemispheres.
Amount of CO2 in the air
at Baring Head
since 1971
Other consequences
Graph showing rise in CO2
plus rise of CO2 in ocean and
the resulting reduction in pH.
The amount of
oxygen in the Air at
Baring Head since
1999 is decreasing –
confirming that the
increase is CO2 is
from burning
Amount of Methane in the Air
carbon.
at Baring Head since 1990
What is
happening
is called the
Enhanced
Greenhouse
Effect.
The extra GHGs
result in more heat
being absorbed
and re-emitted to
Earth’s surface,
warming it.
More exactly:
http://2.bp.blogspot.com/-Ap9_Jg7n35c/VW0U5LTNFXI/AAAAAAAAA5g/Z46jceXDS7Q/s1600/Greenhouse-effect.jpg
The increased greenhouse gases in the atmosphere increases its “effective radiating level” (ERL).
Since the fall in temperature with increasing height in the atmosphere is constant (~6°C/km), and
the temperature at the ERL is constant (-18°C), the temperature at the surface of the earth rises as
greenhouse gases increase. This is called the “enhanced greenhouse effect”.
GHGs from humans From 1970 to 2010.
IPCC AR5 WG1 2014 Figure SPM.1
There is now a global effort
to reverse this rising trend the Paris Agreement on
Climate Change, signed in
New York on 22 April 2016.
Its aim is “Holding the
increase in the global
average temperature to well
below 2 °C above preindustrial levels, and pursuing
efforts to limit the
temperature increase to 1.5
°C above pre-industrial
levels..”,
https://en.wikipedia.org/wiki/Pa
ris_Agreement
Climate change effects are
interrelated and are very
hard to exactly work out. This
can lead to some people
denying that there is such a
thing as Climate change or
Global warming.
https://www.youtube.c
om/watch?v=cjuGCJJU
Gsg
watch this
John Oliver clip.
Why are sea levels rising?
The two major causes are:

thermal expansion caused by the warming
of the oceans (since water expands as it
warms)

the loss of land-based ice (such as glaciers
and ice sheets) due to increased melting
Thermal expansion:
When water heats up, it expands. This means
that the warmer oceans occupy more space.
http://i.telegraph.co.uk/multimedia/archive/02822/001
-KIRIBATI_2822394k.jpg
Sea ice melting:
This doesn’t make the sea level rise. This is because it’s already floating in the
ocean. Take a glass of ice water. As it warms, the ice in the glass melts, but the
total volume of water does not change.
Albedo is the measure of the reflectivity of a surface
A perfectly white reflecting surface has an albedo of 1
A perfectly black absorbing surface has an albedo of 0
A surface looks bright when it reflects
most of the light that hits it e.g. ice
sheets, deserts, some rocks e.g.
limestone.
A surface looks dark when most of
the light is absorbed e.g. ocean, dark
surfaces.
The Sun’s energy is reflected off ice
and back out into space. If ice melts
the solar energy is absorbed by the
earth and ocean surface instead,
warming them up further.
The climate system is influenced by many factors, making it
complicated to understand and difficult to work out exactly what
might happen.
Feedbacks in
the climate
system happen
when these
factors affect
each other.
Positive feedbacks increase temperature
Negative feedbacks decrease temperature
Climate scientists also gain evidence of the
effects of change by looking back into the past
Earth’s climate has changed before; evidence comes from many sources:
Ice cores: Ratio of O2 and C isotopes in ice shows temperature changes; air
bubbles can be analysed to measure past CO2 and CH4 concentrations.
Fossil Pollen: Different plants produce distinctive pollen grains which can be preserved
in sediment cores from ponds, lakes and oceans.
Lake sediments: Composition and sedimentation rates change in response to
environmental conditions. Pollen and phytoplankton show the physical and chemical
conditions of lake water.
Ocean sediment cores: contain plankton whose abundance depends on surface
water temperature and other conditions such as pH.
Wind borne material: Its accumulation at a particular location can provide information
on past windiness and dryness.
Glaciers: Variations in the past size of glaciers can be inferred from rocks and debris,
buried soils and glacial features in the landscape.
Tree ring width: depends on soil moisture, temperature and other growing conditions
and can be used to reconstruct past climates.
Instrument Measurements and written or oral records: NZ only has 150 years of
temperature and other meteorological records. Such records can identify the
influence of any non-climate factors (such as encroaching urban development).
Depletion of the Ozone layer vs Climate Change
These two issues can become very confused in some people’s minds.
Depletion of ozone layer (ozone hole) Climate Change (CC) or Global warming
• The ozone layer is in the stratosphere.
• This ozone is created when high-energy
UV strikes an oxygen molecule – a
natural process.
• Ozone protects us from UV radiation
• Depletion of ozone (the ozone hole) was
caused by long-living chemicals, CFCs,
that humans released into the
atmosphere.
• International agreements such as the
Montreal Protocol have banned the use
of CFCs.
• There is a good chance that the ozone
hole will mend in the near future
• This is a relatively straightforward issue
• Greenhouse gases (GHG) e.g. CO2 are found
in the troposphere.
• GHGs are important for keeping Earth warm
because they form an invisible layer that traps
heat that is radiating away from Earth.
• But extra GHGs are accumulating in the
atmosphere because of human activity.
• So extra heat is being trapped, warming the
surface of the Earth.
• The climate system is affected by many factors
which makes the issue very complex e.g. the
Earth is warming but some parts are getting
colder
• CC can not be easily fixed.
• The ozone layer is a region within the stratosphere
with a high concentration of ozone - generally
between 2 and 8 ppm.
• Ozone is created when high-energy UV strikes a normal
oxygen molecule.
• Ozone in the stratosphere protects us from UV in sunlight by
absorbing most of the incoming UV before it reaches the
ground. It re-radiates the energy as heat, warming the
stratosphere.
The Ozone Hole is a major "thinning" of the
ozone layer in the atmosphere. The hole
appears in the winter over the poles,
especially the South Pole. Certain long-living chemicals that humans released into the
atmosphere, such as CFCs, destroyed ozone by chemical reactions.
International agreements have banned the use of CFCs which is helping mend the hole.
Great sites to visit:
http://thiniceclimate.org/free-resources
https://www3.epa.gov/climatechange/kids/index.html
https://www.niwa.co.nz/education-and-training/schools/students/climatechange-global-warming-and-greenhouse-gases
https://vimeo.com/119312940 Fox Glacier’s spectacular retreat in recent years
Also see two reports from the Royal Society of NZ on Climate implications for NZ,
and A Low Carbon Future for NZ, summarising our situation and what we can do, at:
http://www.royalsociety.org.nz/expert-advice/papers/yr2016